Photochemical hydrobromination of olefins



Patented Feb. 6, 1951 TENT OFFICE PHOTOCHEMICAL HYDROBROMINATION OF OLEFINS Antoine E. Lacomble, New York, N. Y., and Denham Harman, Menlo Park, and William E. Vaughan, Berkeley, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application September 16, 1950, Serial No. 185,327

3 Claims.

The present invention relates to an improved method of reacting hydrogen halides with un- V saturated organic compounds. More particularly, the invention relates to an improvement in the light catalyzed reaction of hydrogen halides with unsaturated organic compounds-whereby cer tain substances are removed from the unsaturate which, when present, interfere with the reaction by filtering out the actinic light.

It is well known that hydrogen halides may be or atoms attached to an unsaturated carbon atom,

low molecular weight.

.the normal addition is the one in which the halogen atom of the hydrogen halide becomes attached to the carbon atom which already contains the largest number of halogen atoms. The opposite situation is known as the abnormal addition. This invention relates to the abnormal addition of hydrogen halides to unsaturated organic compounds.

The patent of William E. Vaughan and Frederick F. Rust, 2,307,552. teaches a method of directing the halogen atom to combine with an unsaturated organic compound in the abnormal manner by catalyzing the reaction with actinic light having a wave length below about 2900 to 3000 A. U. (Angstrom units). This process has been found to work well with relatively pure unsaturated compounds and particularly with those having a However, we have now found that in attempting to apply the process to high molecular weight mixtures containing unsaturated compounds, particularly those pro duced by cracking waxes, the reaction does not proceed with the desired rapidity.

Several factors might contribute to this decreasein reactivity. Some diminution in reactivity might be expected as a consequence of the teric factor, i.- e., the necessity for definite orientation of the olefin at the time of approach of ahalogen atom in order that a fruitful collision be made to form a halogen substituted olefin.

The more complex the olefin, themore specific must be the orientation. Further, it has been found that as the olefin molecule increases in length, the absorption of the actinic radiation increases somewhat. However, it has been found that the decrease in reactivity of the high molecular weight mixtures was too great to be accounted for by steric hindrance or increased light absorption by the olefin.

This is borne out by experiments in which th reactivities of pure olefins (prepared from allyl chloride and the appropriate Grignard reagents) were compared. In these experiments, equal volumes of one molar solution of pure l-octene and 1--tridecene in iso-octane were sealed in separate transparent tubes along with equivalent amounts of hydrogen bromide. The tubes were illuminated with ultraviolet light under identical conditions for a short period of time. Isc-octane was used as a solvent because it is transparent to the radiations capable of dissociating hydrogen bromide. After illumination, the tubes were cooled in liquid nitrogen, opened, and the extent of the reaction determined by titration of the unreacted hydrogen bromide. It was found that the l-octene had reacted only 10-20% faster than the l-tridecene. However, as will be further explained in the examples given hereinafter, when a commercial sample of l-tetradecene distilled from a mixture of cracked wax olefins, in which the olefins consisted exclusively of l-olefins, was treated with hydrogen bromide as in the foregoing example, less than 10% of the desired reaction occurred. Hence, in the light of this experiment and the foregoing one with pure tridecene, it can reasonably be concluded that the relative nonreactivity of commercial olefin fractions is due to the presence of inhibiting impurities.

This invention is not predicated on any theory 'of operation, but it is believed that the suspected impurities act as a light filter and inhibit the reaction and that they are compounds having boiling points so near to that of the olefin that they cannot be readily separated from the olefin by fractionation.

We have now found that by appropriately treating the olefin mixture, the reaction inhibiting compounds may be removed. This may be done by contacting the impure olefin with a selective solvent or with a selective adsorptive agent.

Among selective solvents which may be used are liquid sulphur dioxide, furfural, dimethyl sulfolane, phenol, propane-cresylic acid mixture (commercially known as-the Duo-Sol process), chlorox (c,5'-dichloroethyl ether) and the like. Some of the solvents such as sulfur dioxide and furfural have a strong absorption for actinic radiation, so that if such solvents are used it is important that substantially all of the solvent be removed from the olefin. The preferred. solvents are oxygencentaining selective solvents, and of the solvents listed, sulfur dioxide and furfural are particularly preferred. Extraction with the solvent may be done either batchwise or continuously in a countercurrent extractor such as is well known in the art of refining petroleum products. The extent of such treatment will depend upon the quantity of inhibitors present in the olefin under consideration. Olefins from different sources will vary considerably in their impurity content so that it is impossible to specify an exact treatment. However, the extraction should be .continued until the desired improvement (as hereinafter defined) in light transmission has been achieved. Generally speaking, it has been found that if an olefin is contacted successively six times with an equal volume of fresh selective solvent, the actinic light transmission will be satisfactory for photohydrohalogenation. Residual traces of the selective solvent, if their presence in the raffinate is objectionable, .can be removed by washing the raffinate with water or by like applicable treatments.

Silica gel has been found to be a very effective adsorptive agent in removing the impurities, although other known adsorptive agents such as activated charcoal, kaolin, diatomaceous earth, aluminum hydroxide or oxide, burned magnesium oxide, zeolite or the like may be used. When silica gel is used it has been found effective to pack a column with the gel and to allow the olefin to pass through it. Here again, the treatment should be continued until the desired improvement in actinic light transmission is obtained. The silica gel may be regenerated by washing with methyl or ethyl alcohol and used repeatedly. If the various clays are used the olefin may be agitated with the clay either batchwise or continuously followed with removal of the clay by means of a filter press.

Hereinafter reference will be frequently made to the absorption limit of various olefins and mixtures. This absorption limit may be defined as the Wave length at which a 1 cm. depth of the olefin has an optical density of 0.4. Thus if the absorption limit of an olefin is said to be 2900 A. U., a 1 cm. layer has an optical density of 0.4 to light having a wave length of 2900 A. U. and would have a greater optical density for light of shorter wave length or higher frequency.

In the Vaughan and Rust Patent 2,307,552, it is disclosed that the light used in catalyzing the reaction should have a wave length of below about 3000 A. U. In the present invention it is preferred to treat the olefin so that the absorption limit is 3000 A. U. or below. However, since the absorption imit does not represent an absolute cut-oif but only a rather abrupt reduction in transmission, the olefins may be treated to have an absorptive limit as high as 3200 A. U.

The present invention may be utilized to treat any olefins or derivatives thereof. It has been found that the lower olefins, having less than 9 carbon atoms, may ordinarily be hydrohalogenated without treatment to remove aromatic inhibiting compounds. Nevertheless, such compounds may be treated according to the present invention if they contain contaminates which lower the actinic light transmission. The invention is primarily applicable to olefin mixtures which have been produced by the cracking of hydrocarbon molecules by thermal or catalytic means. The cracked hydrocarbons containing olefins may be fractionated into narrow cuts, each of which contains molecules of substantially the same molecular weight or the mixture of olefins produced may be hydrohalogenated in accordance with this invention. A particularly valuable subclass of olefins consists of the olefins having only a single double bond in the 1 position. According to the present invention, such compounds by abnormal addition yield alpha substituted halides which may be used as such or which may be used as intermediates in the production of still further compounds. For instance, the l-halosubstituted hydrocarbons may be readily hydrolyzed to form normal alcohols.

The hydrohalogenation of the olefins under the influence of ultraviolet light may be effected in the vapor or liquid phase or in a two-phase liquid-vapor system. Inasmuch as the present invention is primarily applicable to hydrocarbons .of relatively high molecular weight, it is ordinarily preferred to perform the hydrohalogenation in the liquid phase. Since the abnormal addition of the hydrogen halides according to the present invention occurs photochemically, no heating is necessary. In fact, in many instances the reaction, although it may be eifected at te r.- peratures of about 25 0., is preferably effected at temperatures which are even below 0 C. Inasmuch as the reaction is highly exothermic, suitable means for cooling the reactor should be provided. Also it has been discovered that the abnormal addition of hydrogen halides, when the reaction is effected under the influence of ultraviolet radiations, proceeds regardless of the presence or absence of a liquid film in the reaction zone.

The following examples illustrate the beneficial effects obtained in hydrohalogenation according to the present invention.

Example I A normally-liquid fraction of the olefins produced by cracking Balik-Papan wax, the fraction comprising predominantly olefins containing 14 carbon atoms, and boiling at 196 C. and under 19 mm. mercury pressure, was used as the starting material. The sample was divided into two 100 cc. portions and one was allowed to percolate through a column (14 x 2.5 cm.) of silica gel. The untreated sample had a refractive index of n =L4545 and an adsorption limit of 4050 A. U. The treated sample had a refractive index of 1.4392 and. an absorption limit of 2960 A. U. The samples were then put in reactors and were chilled to 0 C. and hydrogen bromide was passed through the sample. The initial rates showed some similarity, but the rate of reaction of the untreated sample fell off very rapidly. More than of the silica gel-treated material was converted to normal tetradecyl bromide, whereas during the same period less than 10% of the untreated sample was converted.

The reactor used in the above experiments consisted of a 3 liter flask surrounded by an icesalt bath. Near the bottom of the flask was a sintered glass bubbler for the introduction of the hydrogen bromide, and directly above the Example II Another portion of the C14 cracked wax olefin fraction described in Example I was extracted six successive times with volumes of liquid sulfur dioxide equal to that of the olefin. After such treatment the C14 fractions refractive index and absorption limit were reduced from 1.4545 and 4050 A. U. to 1.4392 and 3200 A. U. With furfural as the selective solvent the refractive index and absorption limit of the C14 fraction were reduced to 1.4394 and about 3200 A. U., respectively. A similar improvement in light transmitting ability was obtained with'dimethylsulfolane. The selective solvent-treated samples of the olefin could be readily photohydrobrominated whereas the untreated olefin did not transmit actinic light sufficiently well to permit the reaction to take place readily.

In some instances it may be desirable to conduct the hydrohalogenation in the presence. of solvents. The solvent selected should be one which is inert to hydrogen halides and which is transparent to ultraviolet radiation. For this purpose the normally liquid hydrocarbons such as heptane, iso-octane and nonane are preferred.

Although the above experiments were conducted with hydrogen bromide, it is to be understood that the invention is applicable to the abnormal addition of the other hydrogen halides such as hydrogen chloride, hydrogen iodide and/or hydrogen fluoride. However, the invention is particularly applicable to the abnormal addition of hydrogen bromide.

This application is a continuation-in-part of our copending application Serial No. 678,284, filed June 21, 1946. I

We claim as our invention:

1. In 'a process for producing alkyl bromides, wherein petroleum wax is subjected to a cracking treatment productive of normally liquid 1- olefins and a separated fraction of the products of the cracking treatment comprising normally liquid l-olefins of substantially the same carbon content and having at least 9 carbon atoms, is hydrobrominated by reaction with hydrogen bromide under the deliberately applied action of actinic light, the improvement which comprises the steps of extracting said separated fraction prior to hydrobromination thereof with liquid sulfur dioxide until said fraction has a light absorption limit of not over about 3200 Angstrom units and then hydrobrominating the extracted separated fraction by reaction with hydrogen bromide under the deliberately applied action of ultraviolet light having a wave length below about 3000 Angstrom units.

2. In a process for producing alkyl bromides, wherein petroleum wax is subjected to a cracking treatment productive of normally liquid 1- olefins and a separated fraction of the products of the cracking treatment comprising normally liquid l-olefins of substantially the same carbon content and having at least 9 carbon atoms, is hydrobrominated by reaction with hydrogen bromide under the deliberately applied action of actinic light, the improvement which comprises the steps of extracting said separated fraction prior to hydrobromination thereof with liquid furfural until said fraction has a light absorption limit of not over about 3200 Angstrom units and then hydrobrominating the extracted separated fraction by reaction with hydrogen bromide under the deliberately applied action of ultraviolet light having a wave length below about 3000 Angstrom units.

3. In a process for producing alkyl bromides, wherein petroleum wax is subjected to a cracking treatment productive of normally liquid 1- olefins and a separated fraction of the products of the cracking treatment comprising normally liquid l-olefins of substantially the same carbon content and having at least 9 carbon atoms, is hydrobrominated by reaction with hydrogen bromide under the deliberately applied action of actinic light, the improvement which comprises the steps of extracting said separated fraction prior to hydrobromination thereof with a liquid selective solvent until said fraction has a light absorption limit of not over about 3200 Angstrom units and then hydrobrominating the extracted separated fraction by reaction with hydrogen bromide under the deliberately applied action of ultraviolet light having a wave length below about 3000 Angstrom units.

ANTOINE E. LACOMBLE. DENHAM HARMAN. WILLIAM E. VAUGHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

3. IN A PROCESS FOR PRODUCING ALKYL BROMIDES, WHEREIN PETROLEUM WAX IS SUBJECTED TO A CRACKING TREATMENT PRODUCTIVE OF NORMALLY LIQUID 1OLEFINS AND A SEPARATED FRACTION OF THE PRODUCTS OF THE CRACKING TREATMENT COMPRISING NORMALLY LIQUID 1-OLEFINS OF SUBSTANTIALLY THE SAME CARBON CONTENT AND HAVING AT LEAST 9 CARBON ATOMS, IS HYDROBROMINATED BY REACTION WITH HYDROGEN BROMIDE UNDER THE DELIBERATELY APPLIED ACTION OF ACTINIC LIGHT, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF EXTRACTING SAID SEPARATED FRACTION PRIOR TO HYDROBROMINATION THEREOF WITH A LIQUID SELECTIVE SOLVENT UNTIL SAID FRACTION HAS A LIGHT ABSORPTION LIMIT OF NOT OVER ABOUT 3200 ANGSTROM UNITS AND THEN HYDROBROMINATING THE EXTRACTED SEPARATED FRACTION BY REACTION WITH HYDROGEN BROMIDE UNDER THE DELIBERATELY APPLIED ACTION OF ULTRAVIOLET LIGHT HAVING A WAVE LENGTH BELOW ABOUT 3000 ANGSTROM UNITS. 